Chemistry of miocene plume tholeiites from northwest Iceland     

J.C. Bailey  A. Noe-Nygaard 《Lithos》1976,9(3):185-201

The earliest (Miocene) plateau basalts of northwest Iceland form an olivine tholeiite series with elevated contents of Ti, K, P, Rb, Ba and Sr. They are closely similar to ‘plume’ tholeiites of the Faeroes (Paleocene-Eocene) and the Reykjanes Peninsula, Iceland (Recent) and confirm the Miocene renaissance in northeast Atlantic plume activity previously suggested on geophysical grounds.It is argued that the elevated contents of Ti, K, etc., are due to the ascent in a plume column of high pressure alkalic magmas and their re-equilibration to low pressure olivine tholeiites largely by additional melting at 10–20 km depth and 1150–1300°C.The 1800 m northwest Iceland sequence lacks stratigraphic variation suggesting random extraction from an extensive melt region with a nearly stable range of P-T-chemical conditions.  相似文献   

Conductivity anomalies: lower crust or asthenosphere?     

R.N. Edwards  R.C. Bailey  G.D. Garland 《Physics of the Earth and Planetary Interiors》1981,25(3):263-272

The indication from surface measurements of a zone of relatively high conductivity (resistivity<200 ohm-m) at depths between 20 and 50 km has become so general over the Earth that regions without this zone can be considered anomalous. However, the depths indicated often span the lower crust and the uppermost mantle, so that before any effect can be definitely attributed to one or the other, the depth resolution in the electromagnetic measurements must be carefully considered. This paper applies the eigenvector decomposition of generalized linear inverse theory to soundings by Schlumberger resistivity, by magnetotellurics, by man-made electromagnetic fields formed by controlled current flow in grounded electric transmission lines, and by natural magnetic field variation studies to improve the bounds on depth, thickness and conductivity of a conductive layer. It is shown that many of the methods are capable of giving the depth to the top of a conductor with remarkable accuracy. Joint inversion of two or more of them offers an advantage in the separation of thickness and conductivity of both conductive and resistive layers. Natural geomagnetic field transfer functions, while accurately mapping the position of the edge of a conductor, do not provide the resolution of the other techniques, largely because the frequencies that can be practically measured at present are much too low.  相似文献   

On the use of anhysteretic remanent magnetization in paleointensity determination     

Monika E. Bailey  David J. Dunlop 《Physics of the Earth and Planetary Interiors》1977,13(4):360-362

The relative intensities of anhysteretic remanent magnetization (RAM) and thermoramanent magnetization (TRM) are strongly dependent on grain size, blocking temperature and applied field, and are poorly predicted by existing theories. Analog techniques that substitute ARM for TRM probably yield adequate relative paleointensities in suites of mineralogically similar rocks, but they yield uncertain estimates of absolute paleointensity.  相似文献   

Scientific objectives of the Solar Mesosphere Explorer mission     

Gary E. Thomas  Charles A. Barth  Elaine R. Hansen  Charles W. Hord  George M. Lawrence  George H. Mount  Gary J. Rottman  David W. Rusch  A. Ian Stewart  Ronald J. Thomas  Julius London  Paul L. Bailey  Paul J. Crutzen  Robert E. Dickinson  John C. Gille  Shaw C. Liu  John F. Noxon  Crofton B. Farmer 《Pure and Applied Geophysics》1980,118(1):591-615

The 1981–82 Solar Mesosphere Explorer (SME) mission is described. The SME experiment will provide a comprehensive study of mesospheric ozone and the processes which form and destroy it. Five instruments will be carried on the spinning spacecraft to measure the ozone density and its altitude distribution from 30 to 80 km, monitor the incoming solar ultraviolet radiation, and measure other atmospheric constituent which affect ozone. The polar-orbiting spacecraft will be placed into a 3pm-3 am Sun-synchronous orbit. The atmospheric measurements will scan the Earth's limb and measure: (1) the mesospheric and stratospheric ozone density distribution by inversion of Rayleigh-scattered ultraviolet limb radiance, and the thermal emission from ozone at 9.6 m; (2) the water vapor density distribution by inversion of thermal emission at 6.3 m; (3) the ozone photolysis rate by inversion of the O₂(¹g) 1.27 m limb radiance; (4) the temperature profile by a combination of narrow-band and wide-band measurements of the 15 m thermal emission by CO₂; and, (5) theNO₂ density distribution by inversion of Rayleighscattered limb radiance at 0.439 m. The solar ultraviolet monitor will measure both the 0.2–0.31 m spectral region and the Lyman-alpha (0.1216 m) contribution to the solar irradiance. This combination of measurements will provide a rigorous test of the photochemical equilibrium theory of the mesospheric oxygen-hydrogen system, will determine what changes occur in the ozone distribution as a result of changes in the incoming solar radiation, and will detect changes that may occur as a result of meteorological disturbances.  相似文献   

A low-Li geochemical province in the NE Atlantic     

J.C Bailey  R Gwozdz 《Lithos》1978,11(1):73-84

Lithium was analysed in 392 basalts and related igneous rocks from the North Atlantic Tertiary-Recent province using activation analysis and ?erenkov counting.Monotonous Li values of 5.5±2 ppm in NE Atlantic basalts define a low-Li geochemical province which has persisted for 60 million years, over 20° of latitude and regardless of basalt type and chemistry. This low-Li province and the increasing Li contents of ocean-ridge tholeiites into the S Atlantic are believed to monitor Li heterogeneity in the underlying mantle.Li, like Na, increases gently during the differentiation of several basalt series. No whole-rock coherence is observed between Li and Mg, K, Rb or Ca. Mantle phlogopite is considered to play an insignificant rôle in controlling the Li levels of NE Atlantic basalts.  相似文献   

Anhydrous melting and crystallization of peralkaline obsidians     

D. K. Bailey  J. P. Cooper  J. L. Knight 《Bulletin of Volcanology》1974,38(2):653-665

Experimental determinations of the dry liquidus temperatures of two pantellerite, and two pantelleritic trachyte glasses in the pressure range 0–2 kilobars, show minima in the liquidus curves between 0.1 and 0.2 kb. The pantellerite minima are 830°–850° C; the trachyte minima are 920°–940° C. At pressures below the minima a separate vapour phase co-exists with liquid, at higher pressures the intrinsic volatiles are completely soluble in the liquid and the liquidus curves have a positivedT/dP. Similar results have been obtained from a range of other pantelleritic glasses, and together with consistent alkali feldspar compositions (from a wide range of experimental conditions) are indicative of a close approach to equilibrium. The form of the liquidus curves above the minima, if rellecting natural conditions, offers a ready explanation of the near-or super-liquidus aspect of many peralkaline lavas. The temperatures in these anhydrous experiments are 100°–150° C higher than those for similar compositions in the presence of excess water. (Also, in the presence of excess water, the crystallization sequences in the natural glasses are profoundly modified, with pyroxene appearing on the liquidus). At lower pressures, feldspar is the liquidus phase in the dry pantellerites, but is joined by quartz around 1 kb, and superseded by quartz at higher pressures. As pantellerites with quartz phenocrysts are uncommon, low pressure equilibration is perhaps normal in these magmas. Feidspar is the usual liquidus phase in the trachytes, except at very low pressures where it is preceded by iron oxide. Preliminary studies at 5 kb indicate that the pantelleritic and trachytic liquidus curves are converging (in the range 950°–1000° C). Crystallization sequences, and the forms and positions of the solidus curves are therefore of vital importance. These, together with the vapour-present/vapour-absent conditions, are currently under investigation.  相似文献   

Recommendations for further studies on the peralkaline oversaturated volcanic rocks     

R. Macdonald  D. K. Bailey  F. Barberi 《Bulletin of Volcanology》1974,38(2):828-860

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The crustal structure beneath Porcupine Ridge as determined by explosion seismology     

R.B. Whitmarsh  J.J. Langford  J.S. Buckley  R.J. Bailey  D.J. Blundell 《Earth and Planetary Science Letters》1974,22(3):197-204

A 200 km long reversed seismic refraction line shot over Porcupine Ridge, a shoal area in the northeast Atlantic jutting out from the continental margin off Ireland, shows that the ridge has a crustal thickness of about 28 km. This result confirms the continental nature of this feature. The seismic data can be interpreted in two ways, one of which suggests the presence of a 6.7-km/sec refractor within the main crustal layer.  相似文献   

Electron temperatures during rapid subauroral ion drift events     

R. J. Moffett  A. E. Ennis  G. J. Bailey  R. A. Heelis  L. H. Brace 《Annales Geophysicae》1998,16(4):450-459

Examples of data from DE-2 satellite instruments are presented. These illustrate the behaviour of plasma parameters in the F-region and adjacent topside ionosphere during rapid sub-auroral ion drift (SAID) events. In particular, a variety of behaviours of the electron temperature (T_e) is demonstrated, both within and equatorward of the SAID region. The Sheffield University plasmasphere-ionosphere model (SUPIM) is used to perform calculations in which a model SAID is applied to a plasma flux tube. The model results indicate that strongly elevated ion temperature (a recognised signature of SAID events) is on occasion sufficient to raise T_e to observed values by ion-electron heat transfer. On other occasions, an additional heat source is required. It is suggested that such a source for the electron gas may be due to interaction between the ring current and the plasmasphere at high altitudes. The magnitude of the downward heat flux is consistent with that necessary to produce sub-auroral red arcs. The resulting strongly heated electron gas causes vibrational excitation of molecular nitrogen in the thermosphere.  相似文献   

Dynamical evolution of cometary asteroids     

N. W. Harris  & M. E. Bailey 《Monthly notices of the Royal Astronomical Society》1998,297(4):1227-1236

We present results from long-term numerical integrations of hypothetical Jupiter-family comets (JFCs) over time-scales in excess of the estimated cometary active lifetime. During inactive periods these bodies could be considered as 'cometary' near-Earth objects (NEOs) or 'cometary asteroids'. The contribution of cometary asteroids to the NEO population has important implications not only for understanding the origin of inner Solar system bodies but also for a correct assessment of the impact hazard presented to the Earth by small bodies throughout the Solar system. We investigate the transfer probabilities on to 'decoupled' subJovian orbits by both gravitational and non-gravitational mechanisms, and estimate the overall inactive cometary contribution to the NEO population. Considering gravitational mechanisms alone, more than 90 per cent of decoupled NEOs are likely to have their origin in the main asteroid belt. When non-gravitational forces are included, in a simple model, the rate of production of decoupled NEOs from JFC orbits becomes comparable to the estimated injection rate of fragments from the main belt. The Jupiter-family (non-decoupled) cometary asteroid population is estimated to be of the order of a few hundred to a few thousand bodies, depending on the assumed cometary active lifetime and the adopted source region.  相似文献